too bad the 30-30 isn't legal in CAS it was almost avaible in the old west

No, not even close, not even out of a rifle, in fact, a .30-30 probably won't meet the 2000 joule at 100 meter standard.

Energy = 1/2 mass x velocity squared.
Use kilograms as your mass unit and meters per second as your velocity unit and the answer will be in joules.
Use slugs as your mass unit and ft per second as your velocity unit and your answer will be in ft-lb.